1. Field of the Invention
The present invention relates to an image processing method and an image processing device for outputting image data to an image output device which records an image on a recording paper, on the basis of image data for multi-color printing.
2. Description of the Related Art
DTP (desktop publishing) has come to be widely used as a way of digitizing in the field of printing processing. In DTP, at a processing device such as a personal computer or a work station or the like, a page layout is prepared by carrying out creation, manipulation, editing, and the like of an image. On the basis of this page layout, preparation of a film for exposing a printing plate is carried out (CEPS), or a press plate for printing is prepared by directly writing the image onto a printing plate (CTP: computer-to-plate).
When proofing and the like are carried out before printing using an actual press plate, a page layout displayed on a monitor is printed by a print-out device such as a page printer or the like by using the WYSIWG function or the like of a processing device.
Usual color printing is carried out by using the four colors (process colors) of cyan, magenta, yellow and black. However, there are cases in which inks of colors different from the process colors (such colors are hereinafter called “spot colors”) are used as needed.
In recent years, in order to keep printing costs down, there are cases in which two-color printing is carried out. At this time, special effects can be achieved by using one process color and a spot color, or by using two spot colors.
Even if an attempt is made to use a spot color at the time of preparing, on a client computer, output data for two-color printing, it is usually the case that, in ordinary applications for DTP (i.e., in software for specific purposes, and devices which store and implement such software), mixing of a spot color and a spot color, or mixing of a spot color and a process color cannot be designated. Thus, data for two-color printing is usually film—outputted by using two process colors.
If process colors are used, mixing of the colors can be easily designated. However, when outputting to an ordinary image processing device, only output which is in the process colors can be obtained. Thus, it is difficult to clearly confirm the finish of the actual printed matter.
In order to overcome this problem, in the client computer, a method is used which utilizes an application for conversion, and which separately generates and prints-out data for output confirmation.
In this method, for example, a pattern of a region in which color data is defined is extracted from document data prepared by using a DTP application. By rewriting this color data, a document of two process colors is converted into colors which are close to two colors using spot colors. In this way, color comprehensive layout output, which is as if spot colors were used, can be obtained even from document data prepared by using two process colors.
However, using a conversion application at the client computer entails preparing another data for color comprehensive layout output, and the data management becomes complicated. Further, when the data prepared by the application is converted, overprinting and trapping information of the original data is lost. Thus, simulations of overprinting and trapping and the like cannot be carried out.
To address this problem, Japanese Patent Application Laid-Open (JP-A) No. 2000-62253 discloses a method for applying a special profile for two-color printing to a CMYK color management function.
In this method, first, predetermined spot color inks used in two-color printing are used, and a color chart is printed by actually using a press plate. By measuring this color chart, a profile for the spot color (a CMYK-L*a*b* look-up table) is prepared. Then, simulation of spot color printing is carried out by realizing CMYK-C′M′Y′K′ conversion using the color management function, by using the profile for the spot color and a profile for the printer (an L*a*b*-C′M′Y′K′ look-up table).
However, in this method, the color chart obtained by combining the two colors which are used must be printed by using the actual spot color inks. This chart must be subjected to color measurement, and a profile must be prepared. The work for preparing the profile must be carried out each time the color which is used is changed. A problem arises in that, in the initial proofreading printing, if the finish is different from the envisaged finish or if changing of the spot color is desired, much work, time and cost is required in preparing a new profile.
Namely, in the method disclosed in JP-A No. 2000-62253, when the combination of colors which are used is changed, work, time and costs, which are equivalent to or greater than those in a case in which a flat-bed proof printing press or the like is used, are required in order to obtain a proof print.